For me, though, the most worrying aspect of political correctness was over the story that recurred with increasing frequency during my last ten years at the BBC — global warming (or ‘climate change’, as it became known when temperatures appeared to level off or fall slightly after 1998). From the beginning I was unhappy at how one-sided the BBC’s coverage of the issue was, and how much more complicated the climate system was than the over-simplified two-minute reports that were the stock-in-trade of the BBC’s environment correspondents.

These, without exception, accepted the UN’s assurance that ‘the science is settled’ and that human emissions of carbon dioxide threatened the world with catastrophic climate change. Environmental pressure groups could be guaranteed that their press releases, usually beginning with the words ‘scientists say?.?.?.?’ would get on air unchallenged.

On one occasion, an MP used BBC airtime to link climate change ­doubters with perverts and holocaust deniers, and his famous interviewer didn’t bat an eyelid.

On one occasion, after the inauguration of Barack Obama as president in 2009, the science correspondent of Newsnight actually informed viewers ‘scientists calculate that he has just four years to save the world’. What she didn’t tell viewers was that only one alarmist scientist, NASA’s James Hansen, had said that.

My interest in climate change grew out of my concern for the failings of BBC journalism in reporting it. In my early and formative days at ITN, I learned that we have an obligation to report both sides of a story. It is not journalism if you don’t. It is close to propaganda.

The BBC’s editorial policy on ­climate change, however, was spelled out in a report by the BBC Trust — whose job is to oversee the workings of the BBC in the interests of the public — in 2007. This disclosed that the BBC had held ‘a high-level seminar with some of the best scientific experts and has come to the view that the weight of evidence no longer justifies equal space being given to the opponents of the consensus’.

The error here, of course, was that the BBC never at any stage gave equal space to the opponents of the consensus.

But the Trust continued its ­pretence that climate change ­dissenters had been, and still would be, heard on its airwaves. ‘Impartiality,’ it said, ‘always requires a breadth of view, for as long as minority ­opinions are coherently and honestly expressed, the BBC must give them appropriate space.’

In reality, the ‘appropriate space’ given to minority views on climate change was practically zero.
Moreover, we were allowed to know practically nothing about that top-level seminar mentioned by the BBC Trust at which such momentous conclusions were reached. Despite a Freedom of Information request, they wouldn’t even make the guest list public.

There is one brief account of the ­proceedings, written by a conservative commentator who was there. He wrote subsequently that he was far from impressed with the 30 key BBC staff who attended. None of them, he said, showed ‘even a modicum of professional journalistic ­curiosity on the subject’. None appeared to read anything on the subject other than the Guardian.

This attitude was underlined a year later in another statement: ‘BBC News currently takes the view that their reporting needs to be calibrated to take into account the scientific consensus that global warming is man-made.’ Those scientists outside the ‘consensus’ waited in vain for the phone to ring.
It’s the lack of simple curiosity about one of the great issues of our time that I find so puzzling about the BBC. When the topic first came to ­prominence, the first thing I did was trawl the internet to find out as much as possible about it.

Anyone who does this with a mind not closed by religious fervour will find a mass of material by respectable scientists who question the orthodoxy. Admittedly, they are in the minority, but scepticism should be the natural instinct of scientists — and the default setting of journalists.

Yet the cream of the BBC’s inquisitors during my time there never laid a glove on those who repeated the ­mantra that ‘the science is settled’. On one occasion, an MP used BBC airtime to link climate change ­doubters with perverts and holocaust deniers, and his famous interviewer didn’t bat an eyelid.

Meanwhile, Al Gore, the former U.S. Vice-President and climate change campaigner, entertained the BBC’s editorial elite in his suite at the Dorchester and was given a free run to make his case to an admiring internal audience at Television Centre.

His views were never subjected to journalistic scrutiny, even when a British High Court judge ruled that his film, An Inconvenient Truth, ­contained at least nine scientific errors, and that ministers must send new guidance to teachers before it was screened in schools. From the BBC’s standpoint, the judgment was the real inconvenience, and its ­environment correspondents downplayed its significance.

At the end of November 2007 I was on duty on News 24 when the UN panel on climate change produced a report which later turned out to contain ­significant inaccuracies, many stemming from its reliance on non-peer reviewed sources and best-guesses by environmental activists.

But the way the BBC’s reporter treated the story was as if it was beyond a vestige of doubt, the last word on the catastrophe awaiting mankind. The most challenging questions addressed to a succession of UN employees and climate ­activists were ‘How urgent is it?’ and ‘How much danger are we in?’

Back in the studio I suggested that we line up one or two sceptics to react to the report, but received a totally negative response, as if I was some kind of lunatic. I went home and wrote a note to myself: ‘What happened to the journalism? The BBC has ­completely lost it.’

A damaging episode illustrating the BBC’s supine attitude came in 2008, when the BBC’s ‘environment ­analyst’, Roger Harrabin, wrote a piece on the BBC website reporting some work by the World ­Meteorological Organization that questioned whether global ­warming was going to continue at the rate ­projected by the UN panel.

A green activist, Jo Abbess, emailed him to complain. Harrabin at first resisted. Then she berated him: ‘It would be better if you did not quote the sceptics’ — something Harrabin had not actually done — ‘Please reserve the main BBC online channel for emerging truth. Otherwise I would have to conclude that you are insufficiently educated to be able to know when you have been psychologically manipulated.’

Did Harrabin tell her to get lost? He tweaked the story — albeit not as radically as she demanded — and emailed back: ‘Have a look and tell me you are happier.’

This exchange went round the world in no time, spread by a ­jubilant Abbess. Later, Harrabin defended himself, saying they were only minor changes — but the sense of the changes, as specifically sought by Ms Abbess, was plainly to harden the piece against the sceptics.

Many people wouldn’t call that minor, but Harrabin’s BBC bosses accepted his explanation.
The sense of entitlement with which green groups regard the BBC was brought home to me when what was billed as a major climate change rally was held in London on a ­miserable, wintry, wet day.
I was on duty on News 24 and it had been arranged for me to ­interview the leader of the Green Party, Caroline Lucas. She clearly expected, as do most environmental activists, what I call a ‘free hit’ — to be allowed to say her piece without challenge.

I began, good naturedly, by observing that the climate didn’t seem to be playing ball at the moment, and that we were having a particularly cold winter while carbon emissions were powering ahead.
Miss Lucas reacted as if I’d ­physically molested her. She was outraged. It was no job of the BBC — the BBC! — to ask questions like that. Didn’t I realise that there could be no argument over the science?
I persisted with a few simple observations of fact, such as there appeared to have been no warming for ten years, in contradiction of all the alarmist computer models.

A listener from one of the sceptical climate-change websites noted that ‘Lucas was virtually apoplectic and demanding to know how the BBC could be making such ­comments. Sissons came back that his role as a journalist was always to review all sides. Lucas finished with a veiled warning, to which Sissons replied with an “Ooh!”’

A week after this interview, I went into work and picked up my mail from my pigeon hole. Among the envelopes was a small Jiffy Bag, which I opened. It contained a substantial amount of faeces wrapped in several sheets of toilet paper.

At the time no other interviewers on the BBC — or indeed on ITV News or Channel Four News — had asked questions about climate change which didn’t start from the assumption that the science was settled.